This invention relates to an insulating protective material effective for protecting electronic and electrical components such as electronic elements and the like.
More particularly it relates to protective material used for protecting elements, contacts, etc. of IC packages and electronic devices including the IC packages used as electronic materials or electronic and electrical components such as electronic elements, e.g., indicator tubes. According to this invention there is provided an insulating protective material which can maintain stable and excellent performances with no elution of ionic substances (referred to as "ionic impurity" hereinafter) present therein by capturing and fixing the ionic impurity by adding a specific hydrous oxide.
Insulating protective materials used for protection of elements or contacts of electronic elements utilizing various functions such as semiconducting functions, dielectric functions, magnetic functions, insulating functions, coloring and decoloring function (e.g., diode, transistor, condenser, liquid crystal, thermistor, IC, LSI, etc) and electronic devices having these elements or indicator tubes are called sealers, casting materials, potting materials, interlaminer maintaining materials, junction coating materials, passivation materials, dipping materials, sealing materials, roller coating materials, drip coating materials and the like depending on their application purposes, devices, positions, means, etc.
As components of these insulating protective materials (referred to as "protective material" hereinafter) there are known such fusion bonding materials as ceramic materials such as low-melting glasses and high-molecular weight materials such as epoxy resin, epoxysilicone resin, silicone resin, phenolic resin. In general, high-molecular weight materials are often used because of their good moldability, their mass-producibility, and because they are inexpensive.
These are seldom used alone and are ordinarily used together with fillers. Typically useful inorganic fillers include lead titanate, fused silica, .beta.-eucryptite, titanium oxide, glass fibers, glass beads and the like.
Properties required for these protective materials are low-temperature and short-time fusibility and hardenability, low expansion or negative expansion against temperature rise, formation of strong sealing power and high insulation property. The insulation property is especially important.
It has been said that various inhibition factors such as migration of ionic impurity in protective materials, moisture absorption of protective materials, charge density at the solid surface of protective materials, etc. are related in a complex manner to the insulation property resulting in bad effects thereon. Furthermore, halogen ions are considered to cause corrosion of electronic elements such as IC elements or lead wires. Many countermeasures for removing these effects have been proposed. Generally, the above effects on protective materials as final products are prevented by selection of raw materials and prevention of contamination in purification and production processes.
Particularly, effects of alkali metal ions (Li.sup.+, Na.sup.+ K.sup.+, etc) and halogen ions (F.sup.-, Cl.sup.-, Br.sup.-, etc) which are ionic impurities cannot be disregarded. Presence of these ions even in an amount of a few ppm is considered to cause reduction of insulation. These ionic impurities are desirably completely eliminated in the process of production of protective materials, but practically it is very severe burden from processing and economic viewpoints to eliminate even the slight amount of the ionic impurities.
The alkali metal ions and halogen ions come from the impurities in inorganic fillers which are a constitutional component of the protective materials such as fused silica, titanium oxide, .beta.-eucryptite, glass fibers, glass beads, etc., but some come from raw materials for organic high molecular weight materials which are another component of the protective materials. For example, an epoxy resin is most commonly used as a component of protective materials. It is synthesized from epichlororhydrin ##STR1## According to this synthesis reaction dehydrochlorination is carried out with a catalyst such as an alkali hydroxide and sodium chloride is produced as a reaction product. The synthesis is performed using excess epichlorohydrin and so there remains unreacted epichlorohydrin in the epoxy resin provided as a component of protective materials. In this case the halogen present as a functional group does not have effect on insulation in chemically bonded state, but the remaining unreacted epichlorohydrin often decomposes under some condition and behaves as an ionic impurity.
Furthermore, sulfur-containing organic high molecular weight compounds such as polyether sulfone ##STR2## polyphenylene sulfide ##STR3## polysulfone sulfide ##STR4## etc. are expected to displace epoxy resins. However, as with epoxy resins, production of these compounds requires organic halogen compounds, e.g., 1,4-dichlorobenzene ##STR5## and dichlorodiphenyl sulfone ##STR6## as starting materials and the synthesis reactions all comprise sodium chloride elimination reaction. In these cases, the produced polyether sulfone, polyphenylene sulfide and polysulfone sulfide, usually contain unreacted halogen compounds, which are decomposed by heat, moisture and the like to produce halogens. For this reason these compounds, though they are effective as a components of protective materials, have not yet been practically used.
On the other hand, some of the fillers which constitute the protective material contain an alkali metal ion as a principal component and such component is known to play a part of the performance of the protective material.
For example, .beta.-eucryptite (LiO.sub.2 .multidot.Al.sub.2 O.sub.3 .multidot.nSiO.sub.2) has a negative expansion property against increasing temperature. Owing to this property attempts have been made to utilize this substance as a filler for protective materials. However, .beta.-eucryptite is also a conductor of lithium ion and lithium ions move in an electric field. From the viewpoint of insulation property of protective materials .beta.-eucryptite must be regarded as an ionic impurity which cause undesirable results.
Since ions present in protective materials move with electrical charge to give electrical conductivity, it is necessary for improving insulation to provide conditions to prevent the migration of ions.